I would say that it depends on the extent of damage - if it has been spotted early like you did jaykay, the milk would likely go down (infection in the mammary gland does not aid milk production!) but then come up again.
It also depends how long lactation had been so far, though. If she is many months away from her previous kidding, I'd say to expect the milk not to go back to the level it was before the mastitis.
Also re. withdrawal, if the label of your injectable says not to use in milk producing animals it means that it is likely stored in other tissues of the body and released later, with more or less amounts ending in the milk. If you are happy to use it after 6 days it is up to you, I would wait a month (30 days is average default withdrawal for medicines that do not report it on the label, unless recent studies prove otherwise).